Summary Of Significant Accounting Policies (Reclassification Out Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	$ 449,132	$ 596,127	$ 824,327	$ 1,120,036
Purchased Gas	81,623	190,600	123,691	317,690
Other Income	3,236	1,388	5,654	2,571
Income Before Income Taxes	(263,717)	21,805	(597,176)	161,705
Income Tax Expense	116,030	(5,136)	260,380	(60,296)
Net Income (Loss) Available for Common Stock	(147,687)	16,669	(336,796)	101,409
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income Before Income Taxes	61,623	54,130	118,793	78,395
Income Tax Expense	(25,763)	(22,917)	(43,769)	(33,006)
Net Income (Loss) Available for Common Stock	35,860	31,213	75,024	45,389
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income [Member] | Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income	388	0	388	0
Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income [Member] | Commodity Contracts [Member] | Gains And Losses On Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operating Revenues	57,914	53,471	114,242	73,508
Purchased Gas	3,530	659	4,450	4,887
Foreign Currency Contracts [Member] | Amount Of Gain Or (Loss) Reclassified From Accumulated Other Comprehensive Income [Member] | Gains And Losses On Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Operation and Maintenance	$ (209)	$ 0	$ (287)	$ 0